Generally, laptop lockups are related to overheating. You might try installing one of the software packages that monitors the temp of your CPU. Preferably one that records a log periodically, so that the record is still there after it locks up and you reboot.
But ten minutes seems awful fast for it to lockup. Does this only happen when using a browser? If so, look for something like an over-growing cache file or something like that.
Heat is certainly a common cause. Do you hear the fans starting up ? Do you keep the laptop on a surface where it can get ventilation as some use theirs sitting on a bed or some such place ?
Next thing you could check is for any faults in XP / Vista Device Manager :
In XP right click on My Computer > Properties > Hardware > Device Manager.
In Vista right click My Computer, and select Manage. Then, from the Computer Management window, select Device Manager.
You will be presented with a ‘tech tree’ of all the components in your laptop - look for any red / yellow warning markers that can suggest a fault / incorrect installation, or incompatible driver.
Failing that - assuming you have an up to date Anti Virus - run a full scan. Best to put the computer in Safe Mode and then run the AV.